1. Field of the Invention
This invention relates to a rock bolt having an expandable tube and a shielded distal end, a method of making such a rock bolt, and a method of using such a rock bolt.
2. Description of Related Art
Rock bolts are used in underground mines, such as coal mines, to support the roof and ribs. Installation of conventional rock bolts involves drilling a borehole into the rock to a desired depth using an elongated drilling tool (termed the drill steel), removing the drill steel from the borehole, optionally inserting adhesive resin cartridges, and retaining the cartridges in the blind end of the borehole while a bolt, optionally bearing an expansion anchor, is installed into the borehole. The free end of the bolt extending out of the borehole is received by a chuck of a bolting machine. The bolting machine rotates the bolt within the borehole to mix the adhesive resin and/or expand the expansion anchor.
Other rock bolts comprise a longitudinally expandable tube that includes a longitudinally extending depression between two curved outer portions where the tube is partially collapsed on itself. The ends of the tube are folded over to create two enclosed cavities in the curved outer portions of the tube while a temporary passageway defined by the depression remains open on the ends. After placing the rock bolt in the pre-drilled borehole, pressurized fluid is delivered into the two cavities to force the depression outward, expand the tube, and compress it against the surrounding rock. Until the expansion has been completed, the ends of the passageway defined by the depression are open so that debris from the borehole can fall into the passageway defined by the depression.